The present invention relates to a carriage apparatus for use in a floppy disk apparatus, which is equipped with a magnetic head and executes the tracking of the head.
Generally, a floppy disk apparatus is designed such that a magnetic head performs a seek operation on a floppy disk to seek a desired track and accesses this track for data read/write operation. There is known a carriage apparatus which uses a lead screw to drive and position a carriage mounted with a magnetic head in order to execute the seek operation.
Conventional carriage apparatuses of this type comprise a carriage equipped with a magnetic head and a guide rail for guiding the carriage. The carriage is constituted by a carriage body of a nearly rectangular shape and a carriage arm disposed above the carriage body, between which a part of a floppy disk is adapted to be inserted. A magnetic head is provided at the distal end portion of each of the carriage body and carriage arm on the side facing the floppy disk. To move the magnetic head in the radial direction of the floppy disk, the guide rail is disposed so that its axis extends in that direction. The carriage is provided with a bearing by which the carriage is guided to the guide rail and supported there. The carriage apparatus further has a lead screw for driving the carriage, which is disposed in parallel to the guide rail and located in a position laterally spaced from the guide rail. The carriage has a side arm protruding from the lateral side thereof, through which the lead screw extends. The lead screw is engaged with a feed nut provided at a tip end portion of the side arm. The lead screw is linked to a stepping motor. With the rotation of the stepping motor, the carriage moves along the guide rail through the lead screw and the feed nut.
In conventional carriage apparatuses thus constituted, in case of tracking the magnetic head, the carriage-driving force, which is generated by the torque of the stepping motor and converted by the lead screw and the feed nut, acts on the carriage in the direction parallel to the guide rail at the position of the feed nut of the side arm. Since this line of action of the carriage-driving force does not pass through the center of gravity of the carriage, there occurs a moment of force about a line perpendicularly intersecting a plane including the line of action of the driving force, which extends nearly in parallel to a face of the floppy disk. Due to a gap between the guide rail and the bearing, the carriage is turned by this moment of force and is therefore moved in an inclined state. Particularly, because of the turning of the carriage in a plane parallel to the face of the floppy disk, the actual position of the magnetic head in the radial direction of the floppy disk is deviated from an intended position which is determined by the rotational angle of the stepping motor. In other words, when the magnetic head is moved outward in the radial direction of the floppy disk, the magnetic head is positioned inside by some distance from the intended position; on the other hand, when the magnetic head is moved in the opposite direction, it is positioned outside from the intended position. Consequently, the conventional floppy disk apparatuses would cause a tracking deviation in the seek operation of the magnetic head, thus causing an error in the read/write operation of the floppy disk apparatus.